Single-Spin Asymmetries at CLAS  Transverse momentum of quarks and spin-azimuthal asymmetries  Target single-spin asymmetries  Beam single-spin asymmetries in  semi-inclusive pion production  exclusive pion production  Summary H. Avakian, L.Elouadrhiri (Jefferson Lab) Conference on Intersections of Particle and Nuclear Physics For the CLAS Collaboration

H. Avakian CIPANP 2003 May212 Parton Distribution Functions generalized to contain information not only on longitudinal, but also on the transverse distribution of partons:  Generalized Parton Distributions (GPD) H, E...  Transverse-momentum dependent (TMD) parton distributions Orbital Angular Momentum and Transverse momentum of quarks SSA are sensitive to the orbital motion of quarks, enable measurements of GPDs and k T -dependent PDFs (TMDs) Spin asymmetries + azimuthal dependence new class of DIS measurements Single-Spin Asymmetries:

H. Avakian CIPANP 2003 May213 - Dependent Parton Distributions f 1, g 1 studied for decades: h 1 and others essentially unknown Gauge invariant definition of TMDs discussed by Collins and Belitsky,Ji & Yuan Nucl.Phys. B , 2003 Twist-2 - dependent PDFs by Mulders et al. opens access to mixed hadron-parton and parton- hadron transitions TMDs appear in sin  and sin2  SSA In polarized semi-inclusive DIS

H. Avakian CIPANP 2003 May214 Polarized Semi-Inclusive DIS Cross section defined by scale variables x,y,z Two fundamental QCD mecha- nisms (Collins and Sivers) identified, to generate SSA: Hadron-Parton/ Parton-Hadron transitions described by distribution and fragmentation functions.

H. Avakian CIPANP 2003 May215 Contributions to σ in ep→e’  X σ for longitudinally polarized leptons scattering off unpolarized protons: Different structure functions can be extracted as azimuthal moments of the total cross section. More spin-dependent azimuthal moments arise for polarized targets

H. Avakian CIPANP 2003 May216 The CLAS Detector Scattering of 5.7 GeV polarized electrons off polarized NH 3 and unpolarized hydrogen  ~8M  + in DIS kinematics, Q 2 >1 GeV 2, W 2 >4 GeV 2, y 0.5  beam polarization 73%  target polarization 72% (f≈0.2) X n

H. Avakian CIPANP 2003 May217 Longitudinally Pol. Target: SSA for  + Target SSA: CLAS (4.3 GeV, and 5.7 GeV ) consistent with HERMES (27.5 GeV) A UL z-dependence also consistent both in magnitude and sign with predictions based on Collins mechanism predictions for Sivers effect from BHS Phys.Lett.B53099,2002 Sivers only interpretation require large A UT

H. Avakian CIPANP 2003 May218 H1H1 Longitudinally Pol Target: SSA for  + SSA: x-dependence CLAS (5.7 GeV) is consistent with predictions for Collins effect from Efremov et al. hep-ph/ ┬ - Collins FF D 1 – unpol. FF sin2  moment (Kotzinian-Mulders asymmetry) is a clean source of Collins SSA x 4 more CLAS data available for analysis P 1 = ± P 2 = ±0.0025

H. Avakian CIPANP 2003 May219 Unpolarized target: x,z factorization studies at 5.7GeV The z distribution for different ranges of Bjorken x No significant variation observed in z dependence for different x ranges. ep → e’   X ( E e =5.7 GeV, M X > 1.1)

H. Avakian CIPANP 2003 May2110 Factorization studies in CFR at CLAS DIS: Q 2 >1 W 2 >4 y<0.85 The separation of CFR with 0.5<z<0.8 is not changing significantly with beam energy. No significant variation observed in z dependence of A LU for different x ranges

H. Avakian CIPANP 2003 May2111 A LU from CLAS 4.3 and 5.7GeV data 4.3 GeV 5.7GeV No significant dependence on beam energy No sign flip in A LU in the exclusive limit (unlike HERMES target SSA) Low M X in average correspond to large z

H. Avakian CIPANP 2003 May2112 Beam SSA: sin  Moment A LU Beam SSA A LU from CLAS at 4.3GeV and HERMES (SPIN-2002) at 27.5 GeV Beam SSA measurements for different beam energies are consistent.

H. Avakian CIPANP 2003 May2113 A LU x-dependence: CLAS 4.3 vs. 5.7 GeV Photon Sivers Effect Afanasev & Carlson (preliminary) 0.5<z< GeV 5.7GeV 4.3 GeV and 5.7 GeV data consistent CLAS preliminary Beam SSA analyzed also in terms of Collins effect by Efremov et al.

H. Avakian CIPANP 2003 May2114 Photon Sivers Effect Target SSA (Brodsky et al.) Beam SSA (Afanasev & Carlson) Essential constituents Light-cone spin wave function of a nucleon Final state interaction from gluon exchange Beam SSA has the same source and provides access to essential parameters with less ambiguities

H. Avakian CIPANP 2003 May2115 Exclusive pions: CLAS 4.3 vs. 5.7GeV Sign flip at z ~ 0.5 At z>0.5 struck quark in pion W 2 >4 GeV 2,Q 2 >1 GeV GeV 5.7 GeV LUND-MC -t < 0.5GeV 2

H. Avakian CIPANP 2003 May2116 Beam SSA A LU : x,t-dependence t=(P N -P N’ ) 2 5GeV 2, Q 2 >2.5GeV 2 ( =3.0GeV 2 >) CLAS PRELIMINARY Beam SSA for exclusive pions may provide access to GPDs -

H. Avakian CIPANP 2003 May2117 Summary Beam spin asymmetries observed for the first time in exclusive  + electroproduction in hard scattering kinematics. No significant dependence on x observed for z dependencies of beam SSA. Kinematic dependencies of beam and target SSA measured for different beam energies are consistent, and can be described by a variety of theoretical models. Combined analysis of SSA for polarized beam and target needed to separate contributions from different mechanisms and extract corresponding distribution functions.

H. Avakian CIPANP 2003 May2118 LUND-MC Studies NH3 dilution factor ( f=0.21) from data is consistent with LUND and simple quark counting (dotted line).

H. Avakian CIPANP 2003 May2119 Beam SSA In similar to polarized target case kinematics, no sign of significant sin2  term in the data

H. Avakian CIPANP 2003 May2120 x,z Factorization for A LU in  + SIDIS at 5.7 GeV 4.3 GeV 5.8GeV No significant variation observed in z dependence of A LU for different x ranges

H. Avakian CIPANP 2003 May Dependent Parton Distributions f 1, g 1 studied for decades: h 1 and others essentially unknown Gauge invariant definition of TMD PDFs discussed by Collins and Belitsky,Ji & Yuan Nucl.Phys. B , 2003 Twist-2 - dependent PDFs by Mulders et al. TMDs appear in sin  and sin2  SSA In polarized semi-inclusive DIS